RCDs can be divided into three types:                ML: The contacts in these devices are Mechanically Latched, and when closed the contacts in these devices will not open in the event of loss of supply.        ELO: The contacts in these devices are Electrically Latched, and the contacts will open on loss of supply and remain Open on restoration of the supply.        ELR: The contacts in these devices are Electrically Latched, and the contacts will open on loss of supply but will Reclose automatically on restoration of the supply.        STEOL (Self Test and End of Life): The STEOL acronym is now widely used for GFCIs and RCDs incorporating a self testing (ST) function that verifies the correct operation of the GFCI/RCD circuit.        
The end of life (EOL) function provides an indication to the user that the RCD is no longer able to provide its protective function. EOL indication can be by audible or visual means (e.g. a buzzer or an LED), and the EOL function may also include automatic opening of the main contacts or automatic reopening of the contacts if they are manually reset. Commonly owned U.S. Pat. Nos. 8,964,340; 8,974,494; as well as US Application No. US 2010/0013491, Hooper describe an RCD with STEOL. The disclosures of such are incorporated herein by reference in their entireties.